Apparatus for treating ores and other solid materials

ABSTRACT

Particulate solid material, after preheating is tumbled in a somewhat downwardly inclined direction through an extended confined treatment zone while a current or stream of treating gas is pressed through the confined zone in the opposite direction. A current of heating gases at the proper temperature is passed upwardly through an extended confined zone to heat the material indirectly. The gas treated particulate material is discharged at a temperature below that at which it would react with atmospheric gases. The apparatus comprises a totally enclosed rotary kiln installation which maintains the solid material at a predetermined temperature by indirect heating means, and having arrangements at its opposite ends fo r the indirect preheating of the solid material prior to entering the kiln at one end, and for the indirect cooling of the material before the discharge thereof at the opposite end of the kiln.

United States Patent 1191 1111 3,838,848 Jaquay et al. 1 Oct. 1, 1974 [54] APPARATUS FOR TREATING ORES AND 2,648,600 8/1953 Reeve 75/1 OTHER SOLID MATERIALS 533 1 ip 432/114 X n erson [75] Inventors: Louis H. Jaquay; Donald R.

Rathbum, both of Pittsburgh P34 Primary Examiner-Gerald A. Dost g L IT S P C Attorney, Agent, or-Firm-Pennie & Edmonds inar asmussen, arien, onn.

[73] Assignee: F. L. Smidth, & C0., New York, ABSTRACT Particulate solid material, after preheating is tumbled [22] Filed: May 12, 1972 in a somewhat downwardly inclined direction through an extended confined treatment zone while a current PP 252,936 or stream of treating gas is pressed through the con- Related Application Data ginetd zone in oppositet directictm. curregt of ea mg gases a e proper empera ure 1S passe up- [62] 32:51: 1969 wardly through an extended confined zone to heat the material indirectly. The gas treated particulate mate- [52 us. or. 266/18, 432/114 FF is i l i f i below that which 51 Int. c1. F27b 7/38 1 g mac ff l d t 581 Field 61 Search 75/34, 33, 37; 266/15, appala 9 "1 0 a y 7 my 266/ 432/1 14 1 16 1 l7 kiln installation which maintains the solid material at a predetermined temperature by indirect heating means, 1-561 111,22: a azines; 12111 2212532.1133? UNITED STATES PATENTS entering the kiln at one end, and for the indirect 7,156 5/1914 Alford 75/37 cooling of the material before the discharge thereof at the opposite end f the kiln ans 1e 1,917,942 7/1933 Kalling et al 75/33 8 Claims, 6 Drawmg Flglll'es 5/ 5/17 I 7254mm mmmml m 3.838.848

am am 4' bi l [N70195 LOUIS H. J'AQUAY DONALD R. RATHBURN AXEL B. AND'ERSEN EINAR L. RASMUSSEN vnzw m ATT RNEYS This is a division, of application Ser. No. 791,454, filed Jan. 15, 1969, now abandoned.

BACKGROUND OF THE INVENTION 1. Field of the Invention.

The treatment of solid materials in particulate form i.e., granulated, powdered, finely divided or the like such as various ores, and apparatus such as rotary kilns for carrying out the treatment thereof.

2. Description of the Prior Art Heretofore, as shown for example in US. Pat. Nos. 1,938,832 and 2,971,751, rotary kilns have been heated by means of a flame maintained within the kiln and in direct contact with the particulate solid material undergoing treatment. The products of combustion of the fuel employed are in direct contact with the solid material. This restricts considerably the type of reaction that can be brought about.

SUMMARY OF THE INVENTION Method of treating particulate solid material with a gas, and apparatus such as a special rotary kiln installation for treating this material. The particulate material can be treated (tumbled) in direct contact with a gas having controlled reducing, oxidizing, or neutral characteristics. The treatment takes place in confined treatment and heating zones from which outside air is excluded. The particulate material is also heated indirectly by a stream of hot gases from the combustion of fuel in a furnace provided for the purpose. The material is preheated to a predetermined temperature, and with the aid of these hot combustion gases is maintained at such temperature for the desired length of residence time, without exposing the particulate solid material to the products of combustion of the heating fuel or to the outside air. The solid particulate material is then cooled before discharging it to the outside air to inhibit reaction therewith. The granular, powdered, finely divided, or other, solid material is herein referred to collectively as particulate material and includes ores such as oxidic ores including those of nickel, cobalt, manganese, iron, zinc, cadmium, copper and aluminum. The particulate material may also include sulfidic ores, examples of which are the sulfides of nickel, cobalt, iron, manganese, lead, zinc, cadmium, copper aluminum and tin.

The invention may be employed in the reduction of ores such as those indicated above whereby the oxygen is removed in whole or in part. The invention may also be employed in the roasting of particulate solid materials such as sulfitic ores whereby materials such as sulfur are driven off in the form of sulfur gases. The drying .of various particulate materials is also included within the scope of the invention. In all of these processes the aim of the invention is to cause them to take place in a controlled atmosphere without the application of direct heat, which might adversely affect the carrying out of the desired treatment.

A rotary kiln is mounted with its axis at a low angle to the horizontal and the particulate solid material to be treated is admitted at the upper end of the kiln and discharged at the lower end. Before entering the kiln the material is subjected to a preheating operation, partly by means of a series of cylinders mounted on the upper end portion of the kiln and enclosed within a stationary housing, and partly within an unlined section of the kiln at its upper end and within the housing. The kiln is heated by means of a single continuous heat radiating pipe which extends from end to end of the kiln, which is supplied with heat at its lower end by means of a suitable furnace, and which discharges at the upper end of the kiln into the stationary housing. The heating gases are confined within this pipe and cannot enter the kiln. Additional heat may be supplied to the stationary housing by an auxiliary furnace.

The material is preheated to a predetermined temperature in the neighborhood of the reaction temperature within this housing and is admitted into the lined section of the kiln which forms a reaction section at approximately the reaction temperature. The preheating zone to reaction temperature may however under some conditions extend somewhat into the lined section of the kiln. The treated particulate material is cooled before being discharged to the atmosphere at the lower end of the kiln by passing through a plurality of cooling cylinders which are mounted circumferentially around the exterior of a portion of the kiln adjacent the discharge end.

The particulate solid material is admitted to the apparatus at the upper end of the kilnthrough a stationary casing, and a second stationary casing at the lower end of the kiln receives the treated solid material from the cooling cylinders. Seals between these casings and the kiln shell prevent ingress of air and egress of gas. The treating gas is caused to enter the kiln through the stationary casing at the lower end of the kiln and after passing through the kiln in the opposite direction to the flow of the solid material this spent reaction gas together with evaporated moisture, and gaseous reaction products leaves the apparatus through an outlet in the stationary casing at the upper end of the kiln.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a side elevation, partly in section, of a rotary kiln installation according to the invention;

FIG. 2 is a vertical section of the lower or left end portion of the apparatus;

FIG. 3 is a similar view of the upper or right end portion of the apparatus;

FIG. 4 is a cross section taken on line 4-4 of FIG.

FIG. 5 is a cross section taken on line 5-5 of FIG. 3; and

FIG. 6 is a cross section taken on line 66 of FIGS. 1 and 3.

DESCRIPTION OF PREFERRED EMBODIMENT A rotary kiln the shell of which is shown at 10 is conventionally supported on longitudinal .I-beams 11 and concrete foundation blocks 12, the axis of the kiln being at a low or small angle to the horizontal as indicated in FIG. 1, with the upper end at the right and the lower end at the left. Shell 10 also has conventional means for permitting and producing its rotation. These include two circular rails 13 surrounding and suitably located with respect to the length of the kiln, each of which rests upon a pair of rollers 1-4, only one roller of each pair being visible. These rollers have supporting shafts arranged parallel with the axis of kiln l0 and appropriately mounted on I-beams 11. An electric motor 15 is arranged to cause continuous rotation of kiln shell through suitable reduction gearing l6 and friction (or spur) gearing 17.

Shell 10 has a double refractory lining 18 the upper end of which terminates at an end supporting ring 19. This ring is spaced from the upper end of shell 10 leaving an unlined section indicated by numeral 20. Lining 18 extends to a closure plate 21 which is secured by welding or otherwise to the lower end of shell 10 and which is provided with a plurality of openings 22 for the treating gas, as will appear later. A ring-shaped plate 23 at the right end of unlined shell section forms the upper end of rotary shell 10.

A plurality of preheating cylinders 24 lying parallel to the axis of the kiln are arranged in a circumferential series about the upper end portion of kiln 10 and rotate therewith. Cylinders 24 are unlined and are closed at their opposite ends, and each cylinder has an inlet opening near its upper end and an outlet opening near its lower end. The inlet openings each have a short neck 25 which is bolted to a flanged connection 26 forming an inlet passage for solid material from the unlined section 20 of shell 10 to the interior of the cylinder.

The discharge opening of each of the cylinders 24 is connected in a similar way through a neck member 27 and a flanged connection 28 with the interior of the lined section of the rotary kiln, connection 28 being sufficiently long to extend through the thickness of lin ing 18. Flanged connections 26 and 28 are firmly secured within their respective openings in shell '10 as by welding. Cylinders 24 are supported on shell 10 by means of the connections just described. As shown, each of cylinders 24 is composed of two short sections connected by an expansion member 29 so as to limit the forces of expansion and contraction to which the supports for the cylinders may be subjected.

A stationary housing 30 is arranged to surround the end portion of kiln 10 as shown in FIGS. 3 and 5 to provide a heating space for supplying heat to the exterior surfaces of the series of cylinders 24 and the unlined section 20 of the kiln. The openings in the vertical walls 31 of housing 30 through which the rotary shell 10 passes may be flanged as indicated at 32 and, if necessary, provided with conventional seals to reduce the tendency for the hot gases within housing 30 to escape.

To rotary kiln 10 is heated by a single radiating tube 33 which extends axially of the kiln from the lower end to the upper end. Heating tube 33 rotates with the kiln and is supplied with hot gases from a furnace 34 at the lower or left end of the apparatus. The connections between this stationary furnace and rotating tube 33 will be described later on. Near its left end tube 33 is sup ported within a central opening in closure plate 21, and intermediate its ends it may be supported by collars in any suitable manner such as indicated at 35 in FIGS. 3 and 6. As shown collar 35 is carried by radial supports 36 extending inwardly from the interior surface of shell 10.

The spent heating gases within heating tube 33 still at an elevated temperature after traveling the length of kiln 10 divide at the right end of the tube and are directed into the interior of housing 30 to heat the cylinders 24 and unlined shell section 20, as mentioned. After circulating within housing 30 these gases are discharged through an opening 37. The radial passages referred to are provided by means of a branched fitting 38 having two radial branches 39, each of which is joined to a flanged connection 40 which is welded into an opening through the wall of shell 10 so that the heating gases are excluded from the shell.

The particulate solid material to be treated within the rotary kiln 10 is fed continuously into a hopper and through a conventional double airlock 40a into a sloping tube 41 which is arranged in a stationary casing 42 at the extreme right or upper end of the kiln. The solid material is discharged from the lower end of tube 41 onto the unlined section 20 of the kiln, and as the kiln 10 rotates the material in part flows through the openings 26 into the rotating preheating cylinders 24, and in part flows directly from the unlined section 20 into the lined portion of the rotary kiln. The material flowing through the cylinders 24 enters the kiln at the left ends of these cylinders and through the fittings 27 and 28. In order to facilitate the entrance of the solid material into the entrances of fittings 26 of cylinders 24 a guide or lifter plate such as shown at 43 may be arranged adjacent each of these intake fittings.

The heat entering housing 30 from the heat radiating tube 33 may be supplemented by means of a furnace 44 (FIGS. 5 and l) appropriately connected to the interior of housing 30. Suitable baffles (not shown) may be arranged within housing 30 to cause adequate absorption of heat by cylinders 24 and unlined section 20 before the spent gases leave through the exit 37.

A labyrinth seal 45 is provided between the rotating end plate 23 at the right end of kiln 10 and the stationary casing 42 in order to prevent either the escape of treating gases from withinthe kiln or the entrance of outside air into the kiln. Because of the length of heating tube 33 and in order to prevent forces of expansion and contraction thereof from damaging the branched fitting 38 a conventional expansion section 46 is placed between the end of tube 33 and fitting 38.

At the lower or left end of kiln 10 a second group of heat transfer cylinders 47 similar to cylinders 24 is arranged. These cylinders 47'however are employed for the purpose of cooling the solid material after it has passed through the treatment zone within shell 10 to a temperature below that at which it would react with gases of the outside atmosphere. Cooling cylinders 47 are mounted on and around the rotating shell 10 in much the same way as cylinders 24. They are each supported by their respective entrance connections 48 and 49, and exit connections 50 and 51. The inner connection 49 is welded within an aperture in shell 10 and extends to the interior surface of lining 18.

The solid material flows into cylinders 47 through the entrance connections 48, 49 while the cylinders are at the bottom or lower portion of their rotation cycle. The exit connections 50, 51 discharge the material from cylinders 47 as they pass the top or upper portion of their cycle at a location to the left or beyond the closure member 21 of the kiln. The inner exit connections 51 are welded within circular apertures in a cylindrical extension 52 of shell 10 which is secured by bolting flanges as indicated to the closure plate 21.

Beyond cylindrical extension 52 to the left there is a stationary casing 53 which may be supported in any suitable manner (not shown). Casing 53 has a large cylindrical internal space 54 and surrounding this there is an airtight labyrinth seal 55 to exclude ambient air from the interior of rotary kiln 10 or to prevent the escape of treating gases. The details of labyrinth seal 55 and also of labyrinth seal 45 at the upper end of the kiln are described in the prior patent hereinbefore referred to. The rotating portion of seal 55 is a ring member 56 which is secured to the left end of cylindrical extension 52.

Communicating with the lower side of cylindrical space 54 there is a discharge pipe 57 for the particulate solid material which has undergone treatment in rotary kiln l0, and at the upper portion of casing 53 there is an intake pipe 58 for the introduction of the treating gas into the kiln l0.

Mounted within the interior of cylindrical space 54 there is a guiding structure 59 which consists of a funnel-shaped outer member 60 and a cylindrical inner member 61 which are spaced from one another and both of which surround an extension 62 of heat rotating tube 33. Funnel member 60 has an integral cylindrical portion 63 at its inner end and at the inner end of cylindrical member 61 there is an integral conical deflector 64. The inner ends of cylindrical portion 63 and conical deflector 64 are welded together throughout their circumferences and thereby members 64 and 61 are supported by member 60. Guiding member 59 including members 60 and 61, is supported by means of a plurality of narrow radial bars 65 which at their outer portions are secured to the inner surface of ring member 56, and at their inner ends are flanged as indicated and welded to the outer surface of funnel member 60. These parts therefore all rotate with kiln l0.

Cylindrical portion 63 has a plurality of openings formed therein which receive the resepctive inner ends of the exit members 51 of cooling cylinders 47. The solid material being discharged from rotary kiln through the cooling cylinders 47 passes downwardly through the exit members 50 and 51 and is deflected to the left by deflector 64 so that it flows through the passageway between members 60 and 61, and at the left of these members descends into the discharge pipe 57.

The treating gas fed through intake pipe 58 flows in the direction of the arrows through the cylindrical space 54 on both the outer and inner sides of the guiding structures 59 and enters the lower end of the kiln 10 through the openings 22. It leaves the upper end of the kiln by an outlet pipe 66 at the top of stationary casing 42. The rotation of kiln 10 produces a tumbling of the solid material (FIG. 6) moving towards the lower end of the kiln from the upper and thus brings the treating gases and solid material into intimate and repeated mutual contact.

It was previously mentioned that a furnace 34 supplies heating gases to the rotating heating tube 33. These hot gases including products of combustion flow out of the furnace pipe 67 into the left end of extension 62 of the heating tube 33. Extension 62 is connected with tube 33 by an expansion connection 68 and both rotate with tube 33 and kiln 10. To permit such rotation the left end of extension 62 is received within a Sta tionary seal 69 mounted at the end of furnace pipe 67 and supported in an inlet connection 70 which projects centrally from the left of stationary casing 53. The expansion members 46 and 68 associated with rotating tube 33 absorb the longitudinal expansion of this tube and also of its extension 62. The two sections of each of the cooling cylinders 47 also include an expansion connection as shown at 71 for the same purpose.

The cooling cylinders 47 mounted on rotating kiln 10 are cooled by their movement through the ambient air. Under certain circumstances however the solid mate rial passing through these cylinders may be cooled to a greater extent by providing additional air circulation over the rotating cylinders 47 as for example by means of one or more power driven fans. Also should even greater cooling be desired a water spray may be applied to rotating cylinders 47 as shown and described in the patent hereinbefore mentioned.

The above description of the present invention has been made with respect to the kiln construction and method of operation which is at present preferred. It is to be understood that various changes may be made without departing from the scope of the invention as set forth in the following claims.

I claim:

1. In an apparatus for treating particulate solid material with a gas, the combination which comprises:

a. a rotary kiln shell having a refractory lining and having its axis arranged at a relatively low angle to the horizontal for the tumbling therethrough of a body particulate solid material from the upper to the lower end of the kiln;

b. a stationary casing at each end of the rotary kiln shell:

1. the casing at the lower end of the shell having a passage therethrough for feeding a current of treating gas into the kiln shell; and

2. the casing at the upper end of the kiln shell having a passage for the exit of the treating gas, and including means for feeding the particulate soldi material into the kiln shell;

c. airtight seals between each casing and the adjacent end of the shell to prevent ingress of outside atmosphere and egress of the treating gas;

d. a radiant heating tube for hot gases extending from end to end within the shell rotating therewith and constructed to prevent communication between the interior of the tube and the shell interior;

e. means associated with the stationary casing at the lower end of the shell for supplying heating gases to the heating tube;

f. means associated with said casing for discharging the gas treated particulate material from the apparatus;

g. means for cooling the gas treated particulate material including a series of cooling ducts associated with the stationary casing at the lower end of the kiln shell and extending lengthwise of the kiln for cooling the gas treated particulate material to a temperature below that at which it would react with oxygen in the open atmosphere; and

h. means associated with said cooling ducts for delivering the gas treated particulate material from the interior of the kiln shell to the cooling ducts and means for delivering the material from the cooling ducts to the stationary casing for discharge to the atmosphere.

2. In an apparatus for treating particulate solid material with a gas, the combination with comprises:

a. a rotary kiln shell having a refractory lining and having its axis arranged at a low angle to the horizontal for the tumbling therethrough of a body particulate solid material from the upper to the lower end of the kiln;

b. a stationary casing at each end of the rotary kiln shell:

1. the casing at the lower end of the shell having a passage therethrough for feeding a current of treating gas into the kiln shell; and

2. the casing at the upper end of the kiln shell having a passage for the exit of the treating gas, and including means for feeding the particulate solid material into the kiln shell;

c. airtight seals between each casing and the adjacent end of the shell to prevent ingress of outside atmo sphere and egress of the treating gas;

d. a heating tube for hot gases extending from end to end within the shell rotating therewith and constructed to prevent communication between the interior of the tube and the shell interior;

e. means associated with the stationary casing at the lower end of the shell for supplying heating gases to the heating tube;

f. means associated with said casing for discharging the gas treated particulate material from the apparatus; and

g. means associated with the stationary casing at the lower end of the shell for cooling the gas treated particulate material to a temperature below that at which it would react with oxygen in the open atmosphere comprising a series of cylinders extending lengthwise of the kiln shell and fixed to the exterior thereof in circumferential series, each of said cylinders having a conduit near its upper end communicating with the interior of the kiln shell, and a conduit at its lower end communicating with the interior of the stationary casing at the lower end of the shell for delivering the indirectly cooled gas treated particulate material to the interior of said casing for discharge to the atmosphere.

3. Apparatus according to claim 2 in which the upper end of the kiln shell has a section without refractory lining and a. a plurality of cylinders arranged lengthwise of the kiln shell and fixed to the upper end portion thereof in a circumferential series, each of said cylinders having:

I. a conduit near its upper end connected to the unlined section of the kiln shell; and

2. a conduit near its lower end connected to the interior of the lined portion of said shell close to its upper end, particulate solid material being fed into the said unlined section of the kiln shell and in part moving from said section into the lined portion of the kiln shell, and in part moving into and through the respective heating cylinders and thus into the lined section of the kiln shell, and

b. means for applying external heat to the series of heating cylinders and unlined section of the kiln shell so as to preheat the particulate material before entering the lined section of the kiln shell.

4. Apparatus according to claim 3 wherein a closed hood is arranged to surround the series of heating cylinders and the unlined section of the kiln shell, and means for supplying heating gases to said hood for indirectly preheating the material in said cylinders and said unlined shell section.

5. Apparatus according to claim 4 in which the upper end portion of the heating tube within the kiln shell is connected to deliver the heating gases therefrom into said hood so as to thereby indirectly preheat the particulate material in said cylinders and the unlined section of said shell.

6. Apparatus according to claim 5 in which a heating furnace is connected to said hood to supply heating gases thereto in addition to those supplied by the heating tube for the kiln shell.

7. In an apparatus for treating particulate solid material with a gas, the combination including a rotary kiln shell having a refractory lining and having its axis arranged at a low angle to the horizontal for the tumbling therethrough of a body of particulate solid material from the upper to the lower end of the shell, means for feeding the material to the upper end of the shell, and means for removing the tumbled product from the lower end of the shell, the improvement in combination therewith which comprises a stationary casing at each end of the rotary kiln shell, a single radiant tube for heating the kiln extending centrally of the kiln shell from end to end thereof, a furnace at one end of the shell for supplying heating gases to the tube, means for cooling the gas treated particulate material including a series of cooling ducts associated with the stationary casing at the lower end of the kiln shell and extending lengthwise of the kiln for cooling the gas treated particulate material to a temperature below that at which it would react with oxygen in an open atmosphere, means associated with said cooling ducts for delivering the gas treated particulate material from the interior of the kiln shell to the cooling ducts and means for delivering the material from the cooling ducts to the stationary casing for discharge to the atmosphere, and means at the opposite end of the shell for conveying the spent heating gases away.

8. In an apparatus for treating particulate solid material with a gas including a rotary kiln shell having a re fractory lining and having its axis arranged at a low angle to the horizontal for the tumbling therethrough of a body of particulate solid material from the upper to the lower end of the shell, means for feeding the material to thp upper end of the shell, and means for removing the tumbled product from the lower end of the shell, the improvement in combination therewith which comprises a single radiant tube for heating the kiln extending centrally of the kiln shell from end to end thereof, a furnace at one end of the shell for supplying heating gases to the tube, means at the opposite end of the shell for conveying away the spent heating gases which comprises a stationary hood surrounding the end portion of the shell, and two branch tubes extending in opposite directions crosswise of the shell within the hood, the inner ends of such tubes being connected to the central heating tube and the outer end portions of the tubes extending through the kiln shell and discharging into the hood. 

1. In an apparatus for treating particulate solid material with a gas, the combination which comprises: a. a rotary kiln shell having a refractory lining and having its axis arranged at a relatively low angle to the horizontal for the tumbling therethrough of a body particulate solid material from the upper to the lower end of the kiln; b. a stationary casing at each end of the rotary kiln shell:
 1. the casing at the lower end of the shell having a passage therethrough for feeding a current of treating gas into the kiln shell; and
 2. the casing at the upper end of the kiln shell having a passage for the exit of the treating gas, and including means for feeding the particulate soldi material into the kiln shell; c. airtight seals between each casing and the adjacent end of the shell to prevent ingress of outside atmosphere and egress of the treating gas; d. a radiant heating tube for hot gases extending from end to end within the shell rotating therewith and constructed to prevent communication between the interior of the tube and the shell interior; e. means associated with the stationary casing at the lower end of the shell for supplying heating gases to the heating tube; f. means associated with said casing for discharging the gas treated particulate material from the apparatus; g. means for cooling the gas treated particulate material including a series of cooling ducts associated with the stationary casing at the lower end of the kiln shell and extending lengthwise of the kiln for cooling the gas treated particulate material to a temperature below that at which it would react with oxygen in the open atmosphere; and h. means associated with said cooling ducts for delivering the gas treated particulate material from the interior of the kiln shell to the cooling ducts and means for delivering the material from the cooling ducts to the stationary casing for discharge to the atmosphere.
 2. the casing at the upper end of the kiln shell having a passage for the exit of the treating gas, and including means for feeding the particulate soldi material into the kiln shell; c. airtight seals between each casing and the adjacent end of the shell to prevent ingress of outside atmosphere and egress of the treating gas; d. a radiant heating tube for hot gases extending from end to end within the shell rotating therewith and constructed to prevent communication between the interior of the tube and the shell interior; e. means associated with the stationary casing at the lower end of the shell for supplying heating gases to the heating tube; f. means associated with said casing for discharging the gas treated particulate material from the apparatus; g. means for cooling the gas treated particulate material including a series of cooling ducts associated with the stationary casing at the lower end of the kiln shell and extending lengthwise of the kiln for cooling the gas treated particulate material to a temperature below that at which it would react with oxygen in the open atmosphere; and h. means associated with said cooling ducts for delivering the gas treated particulate material from the interior of the kiln shell to the cooling ducts and means for delivering the material from the cooling ducts to the stationary casing for discharge to the atmosphere.
 2. In an apparatus for treating particulate solid material with a gas, the combination with comprises: a. a rotary kiln shell having a refractory lining and having its axis arranged at a low angle to the horizontal for the tumbling therethrough of a body particulate solid material from the upper to the lower end of the kiln; b. a stationary casing at each end of the rotary kiln shell:
 2. the casing at the upper end of the kiln shell having a passage for the exit of the treating gas, and including means for feeding the particulate solid material into the kiln shell; c. airtight seals between each casing and the adjacent end of the shell to prevent ingress of outside atmosphere and egress of the treating gas; d. a heating tube for hot gases extending from end to end within the shell rotating therewith and constructed to prevent communication between the interior of the tube and the shell interior; e. means associated with the stationary casing at the lower end of the shell for supplying heating gases to the heating tube; f. means associated with said casing for discharging the gas treated particulate material from the apparatus; and g. means associated with the stationary casing at the lower end of the shell for cooling the gas treated particulate material to a temperature below that at which it would react with oxygen in the open atmosphere comprising a series of cylinders extending lengthwise of the kiln shell and fixed to the exterior thereof in circumferential series, each of said cylinders having a conduit near its upper end communicating with the interior of the kiln shell, and a conduit at its lower end communicating with the interior of the stationary casing at the lower end of the shell for delivering the indirectly cooled gas treated particulate material to the interior of said casing for discharge to the atmosphere.
 2. a conduit near its lower end connected to the interior of the lined portion of said sHell close to its upper end, particulate solid material being fed into the said unlined section of the kiln shell and in part moving from said section into the lined portion of the kiln shell, and in part moving into and through the respective heating cylinders and thus into the lined section of the kiln shell, and b. means for applying external heat to the series of heating cylinders and unlined section of the kiln shell so as to preheat the particulate material before entering the lined section of the kiln shell.
 3. Apparatus according to claim 2 in which the upper end of the kiln shell has a section without refractory lining and a. a plurality of cylinders arranged lengthwise of the kiln shell and fixed to the upper end portion thereof in a circumferential series, each of said cylinders having:
 4. Apparatus according to claim 3 wherein a closed hood is arranged to surround the series of heating cylinders and the unlined section of the kiln shell, and means for supplying heating gases to said hood for indirectly preheating the material in said cylinders and said unlined shell section.
 5. Apparatus according to claim 4 in which the upper end portion of the heating tube within the kiln shell is connected to deliver the heating gases therefrom into said hood so as to thereby indirectly preheat the particulate material in said cylinders and the unlined section of said shell.
 6. Apparatus according to claim 5 in which a heating furnace is connected to said hood to supply heating gases thereto in addition to those supplied by the heating tube for the kiln shell.
 7. In an apparatus for treating particulate solid material with a gas, the combination including a rotary kiln shell having a refractory lining and having its axis arranged at a low angle to the horizontal for the tumbling therethrough of a body of particulate solid material from the upper to the lower end of the shell, means for feeding the material to the upper end of the shell, and means for removing the tumbled product from the lower end of the shell, the improvement in combination therewith which comprises a stationary casing at each end of the rotary kiln shell, a single radiant tube for heating the kiln extending centrally of the kiln shell from end to end thereof, a furnace at one end of the shell for supplying heating gases to the tube, means for cooling the gas treated particulate material including a series of cooling ducts associated with the stationary casing at the lower end of the kiln shell and extending lengthwise of the kiln for cooling the gas treated particulate material to a temperature below that at which it would react with oxygen in an open atmosphere, means associated with said cooling ducts for delivering the gas treated particulate material from the interior of the kiln shell to the cooling ducts and means for delivering the material from the cooling ducts to the stationary casing for discharge to the atmosphere, and means at the opposite end of the shell for conveying the spent heating gases away.
 8. In an apparatus for treating particulate solid material with a gas including a rotary kiln shell having a refractory lining and having its axis arranged at a low angle to the horizontal for the tumbling therethrough of a body of particulate solid material from the upper to the lower end of the shell, means for feeding the material to thp upper end of the shell, and means for removing the tumbled product from the lower end of the shell, the improvement in combination therewith which comprises a single radiant tube for heating the kiln extending centrally of the kiln shell from end to end thereof, a furnace at one end of the shell for supplying heating gases to the tube, means at the opposite end of the shell for conveying away the spent heating gases which comprises a stationary hood surrounding the end portion of the shell, and two branch tubes extending in opposite directions crosswise of the shell within the hood, the inner ends of such tubes being connected to the central heating tube and the outer end portions of the tubes extending through the kiln shell and discharging into the hood. 